Intro

Precision bench-top multimeters from Keithley we already studied and even repaired before, which was covered in Model 2001 article and Model 2002 article. But it’s first time we have chance to meet rare Model 2001M, which was not shown before anywhere on web.

Index “M” likely comes from *M*ilitary-version, which is hinted by extended documentation kit, and remarks about calibration in USA Navy documents, for example on FBO.gov website. Of course, I could be wrong, and that stands just for (Modified), as it’s is adapted to modern components for production purposes. Not a secret that Keithley’s 200х series instruments were developed over two decades ago, and some of components used in their design are long time obsolete. There are semiconductor enterprises that did not last so long, as these meters do!

Exterior, construction

This model looks completely identical to usual 2001, all buttons, interface, labels are same. For those who did not work with Keithley 200x series gear, these instruments are bench-top type with possible rack-mount installation into standard 19” rack. Their dimensions are 2U height, and half-width, so two units can be installed into single 2U-height space.

Rear panel also shows no difference. Serial number of meter is 1411110, starts with one, similar to ours Model 2002 (which was manufactured in 2007). This already gives us a hint that instrument was manufactured not long time ago, which we will be able to determine more accurately by looking to components date codes.

So, let’s tear it apart and take a look what it have inside.

2001-M retail package

It’s worth a look on complete documentation package, which comes with 2001M:

User interface difference

Main menu and all functions are same, except one single difference: extra mode for ACV measurement – RMS-AVG. This mode is absent on usual Model 2001 version firmwares.
I did few photos to compare menu configuration for ACV function. On the right – DMM with firmware version 2001 A08, on the left – 2001M B17

Operation

In DCV mode 2001M DMM, just like most of others benchtop multimeters, have high input impedance on 20V and lower ranges:

That’s why if input terminals are floating and not connected to signal meter will read some random charge values. That’s is completely normal and not a reason to alarm user, as it’s just picking up static electricity around and charging up small but existing capacitance on input networks of meter itself. This is typical behavior of high-impedance circuits and most of high-end multimeters have this behavior.

To confirm that everything works just fine, you can apply signal or connect 10Meg resistor to input and should see correct stable reading. Model 2001 also have ability to switch between front or rear terminals, so pay attention to correct input location before you do your measurements.

There is easy way to read and backup calibration ROM as well, using external programmer, such as TL866. Procedure and connections shown on photograph below.
To read firmwares we used I2C programmer and held CPURESET signal low during programmer readout (TP602 shorted to DGND):

It’s wise to backup calibration ROM before attempting own recalibration or sending unit to service, just in case.

For those who want upgrade their 2001 to 2001M, I tried to flash usual Model 2001 with digital board revision K (two ROM chips) with this firmware 2001M B17, and everything went well. Meter was detected as 2001M and all functions were operation correctly. No recalibration was required.

If you have another Keithley Model 2001M firmware’s (or any other Keithley instrument firmware), please upload here.

Internal construction

After cover removal, we can see analog board with all magic on it. Everything is very similar to old Model 2001 units, except few details, which we cover later here.

Input voltage selection circuitry and earth-referenced supply is identical to old revisions. Bootstrap supply with capacitors C114-117 also did not had any change, compared to old units. Electrolytic capacitors are made by Nichicon, series VZ, design to operate with temperatures up to +105°С. That is very needed, as caps located just next to hot linear regulators and transformer.

AC measurement block is based around TrueRMS function of Analog AD637JR, which is completely repeated after original design and used in 2001М without changes, as well as in 8½-digit 2002.

Film capacitors C557,C553 are now SMD-type. PCB location for wired version also retained on both, so either type is possible.

Instead of optocouplers TLP582 found in old meters, this one have little board with model number 2001-152A and pair of 110 Mbps 4-channel isolation ICs NVE IL717. Similar module we already saw in Model 2002 multimeter, with different number 2002-132-01A (shown on right photo)

Reed relays are manufactured by American Relays, except K300.

К300 relay now replaced to shielded reed relay from Taiwanese company IC-HI Technology Co.,Ltd.. Relay model is TPM 108D-1A11N2-61. Interesting to note, that their location is within 5 minute walk from our xDevs.com lab.

Resistor divider R607 (9.9 MOhm / 100 KOhm) is now built using pair of alumina-based precision stable CADDOCK resistors, TF050R TF-255 and TF020R, glued together to equalize temperature of divider. This helps to improve ratio stability and tracking of such divider, and reduce errors from temperature variations.

Ohms current sources and range switching circuitry did not change as well, same old Vishay foil resistors.

There are few extra parts, such as transistors Q550, Q552 next to guard circuit driver U331.

Main +6.95V VREF is our old friend, selected LM399. This chip have internal heater and thermostat circuit, so it enjoys very low tempco and excellent long-term stability, which is crucial for such high-end multimeter.

Additional analog board photos:

Let’s take a look on digital board.

This board already familiar, as we reviewed this platform before in Model 2001 and Model 2002.

ADC board module marked as 2001-162N, Revision N

This multimeter using fresh new ADC module, with modern TQFP-packaged CPLD or FPGA from ACTEL. If anyone have idea which model that chip is – please let us know.

Front panel board and keyboard

Final test and check

Hope you enjoy this prompt review and all suggestions are welcome in comments